Method for performing two wafer preparation operations on vertically oriented semiconductor wafer in single enclosure

ABSTRACT

Methods for preparing semiconductor wafers are provided. A method includes disposing a pair of wafer preparation assemblies in an opposing relationship in an enclosure. Each of the wafer preparation assemblies having a first wafer preparation member and a second wafer preparation member. The method includes disposing a semiconductor wafer between the wafer preparation assemblies in a vertical orientation and rotating the wafer. The method also includes orienting the wafer preparation assemblies such that the first wafer preparation members contact opposing surfaces of the rotating wafer in an opposing relationship, and orienting the wafer preparation assemblies such that the second wafer preparation members contact opposing surfaces of the rotating wafer in an opposing relationship.

BACKGROUND OF THE INVENTION

The present invention relates generally to semiconductor fabricationand, more particularly, to methods for preparing semiconductor wafers inwhich preparation operations are performed on a vertically orientedwafer. The preparation is configured to take place in a single enclosureapparatus.

In the fabrication of semiconductor devices, a variety of waferpreparation operations are performed. By way of example, these waferpreparation operations include cleaning operations andpolishing/planarization operations, e.g., chemical mechanicalplanarization (CMP). One known polishing/planarization technique usesplatens with planetary polishing motion. One disadvantage of thistechnique is that it requires multi-step procedures, which aretime-consuming and relatively expensive. Another disadvantage of thistechnique is that it tends to produce wafers having surfaces that sufferfrom a relatively high degree of topographic variations.

Another known polishing/planarization technique involves circumferentialpolishing. In one known circumferential polishing system, a wafer isrotated in a vertical orientation by wafer drive rollers. As the waferis rotated, a pair of cylindrical polishing pads is brought into contactwith the opposing surfaces of the wafer. The polishing pads are mountedon counter-rotating mandrels disposed on opposite sides of the waferbeing processed. The mandrels span across the diameter of the wafer soas to pass over the wafer center. The rotation of the mandrels causes arotary pad motion perpendicular to the wafer diameter in acircumferential direction. During the polishing operation, nozzlesdirect sprays of liquid, e.g., an abrasive slurry, a chemical solution,or a rinse solution, on the opposing surfaces of the wafer.

One drawback of this known circumferential polishing system is that itprovides only circumferential polishing motion. As such, the relativevelocity of each pad is not uniform across each wafer surface, with thevelocity near the wafer edge being greater than the velocity near thewafer center. This is problematic because it not only results in thecreation of circumferential residual scratches on each of wafersurfaces, but also results in a more wafer material being removed fromthe center portion of the wafer than near the perimeter due to thegreater dwell time experienced by the center portion of the wafer. As aconsequence of this nonuniform material removal rate, each of theopposing surfaces of the wafer tends to have a flared contour, i.e., acontour in which the central portion is depressed relative to the edgeportions. As the semiconductor industry moves toward the use of smaller,e.g., 0.18 μm and smaller, feature sizes, such flared contours areundesirable.

In view of the foregoing, there is a need for a method and apparatus forcircumferential wafer preparation that minimizes the creation ofcircumferential residual scratches, provides processed wafers havedesired surface contours, and enables multiple wafer preparationoperations to be performed on a wafer without moving the wafer betweenstations.

SUMMARY OF THE INVENTION

Broadly speaking, the present invention fills this need by providingmethods for preparing wafers.

In accordance with one aspect of the present invention, a method forpreparing a semiconductor wafer is provided. The method includesdisposing a pair of wafer preparation assemblies in an opposingrelationship in an enclosure. Each of the wafer preparation assemblieshaving a first wafer preparation member and a second wafer preparationmember. The method includes disposing a semiconductor wafer between thewafer preparation assemblies in a vertical orientation and rotating thewafer. The method also includes orienting the wafer preparationassemblies such that the first wafer preparation members contactopposing surfaces of the rotating wafer in an opposing relationship andorienting the wafer preparation assemblies such that the second waferpreparation members contact opposing surfaces of the rotating wafer inan opposing relationship.

In accordance with another aspect of the present invention, a method forpreparing a semiconductor wafer is provided. The method includesdisposing a semiconductor wafer in a vertical orientation in anenclosure. A first wafer preparation operation is performed on the waferin the enclosure using a first pair of wafer preparation members, andthen a second wafer preparation operation is performed on the wafer inthe enclosure using a second pair of wafer preparation members.

In yet another aspect of the invention, a method for polishing asemiconductor wafer is provided. This method includes disposing asemiconductor wafer in a vertical orientation in an enclosure androtating the wafer. A first polishing operation is performed on therotating wafer in the enclosure using a first pair of cylindricalpolishing pads, and then a second polishing operation is performed onthe rotating wafer in the enclosure using a second pair of cylindricalpolishing pads.

The advantages of the present invention are many and substantial. Mostnotably, the ability to perform two separate preparation operations in asingle enclosure removes the need to move a wafer to multiple stationsto accomplish a desired preparation recipe. Also, the less a wafer needsto be transported between modules, the less likelihood it will be thatthe wafer will be exposed to contaminants or particulates in thetransfer.

It is to be understood that the foregoing general description and thefollowing detailed description are exemplary and explanatory only andare not restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute partof this specification, illustrate exemplary embodiments of the inventionand together with the description serve to explain the principles of theinvention.

FIG. 1 is an end elevation view of a wafer preparation apparatus inaccordance with one embodiment of the invention.

FIG. 2 is a side elevation view of the wafer preparation apparatus shownin FIG. 1 that shows the right-hand drive casing and its associatedmandrels and polishing pads in cross section, and further shows a wafer(in phantom) supported by the wafer drive roller assembly.

FIG. 3 is an end elevation view of the wafer preparation apparatus shownin FIG. 1 that shows the drive casings in a range of neutral positionsin which the polishing pads are out of contact with a wafer and engageoptional pad conditioners mounted to the walls of the housing.

FIG. 4A is an elevation view of the wafer preparation apparatus shown inFIG. 1 that shows the wafer preparation drive assembly, the levers forpivoting the wafer preparation assemblies, and the linear actuator forpivoting the pivot levers, all of which are disposed outside of thehousing.

FIG. 4B is a more detailed view of the levers and the linear actuatorshown in FIG. 4A in which the actuator rod is shown in its upward,extended position.

FIG. 5A is a cross-sectional view of a wafer preparation assembly, inwhich a self-aligning mandrel having a pad is combined with a brush, inaccordance with an alternative embodiment of the invention.

FIG. 5B is a more detailed view of a self-aligning mandrel assemblyshown in FIG. 5A that focuses on the region proximate to shell centerfulcrum.

FIG. 6 is a graph that shows the amount of wafer material removed versusradial location across the wafer face for four test wafers subjected toconventional centerline polishing.

FIGS. 7A and 7B together show the angular distribution of wafer materialremoved from four test wafers subjected to conventional centerlinepolishing.

FIGS. 8A and 8B are graphs showing the wafer material removal rate (A/m)versus position across the wafer for test wafers polished at the wafercenterline only in accordance with conventional practice.

FIGS. 9A and 9B are graphs showing the wafer material removal rate (A/m)versus position across the wafer for test wafers polished using anoff-diameter polishing method in accordance with one embodiment of theinvention.

FIG. 10 shows a three-dimensional diagram of a wafer preparation stationin accordance with one embodiment of the invention.

FIGS. 11A and 11B illustrate in greater detail the wafer preparationapparatus in accordance with one embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Several exemplary embodiments of the invention will now be described indetail with reference to the accompanying drawings.

The following embodiments describe methods as well as apparatus that canbe used in the preparation of substrates. Such substrates can include,for example, semiconductor wafers of any size, such as 200 mm wafers,300 mm wafers (and smaller or larger wafers). In the followingdescription, the preparation apparatus of the invention is described inconnection with the preparation of wafers. It should be understood,however, that the preparation apparatus also can be used to prepareother substrates such as hard disks and the like. Preparation operationsinclude, for example, buffing, chemical mechanical polishing (CMP),scrubbing (as is done in wafer cleaning), etching, and rinsing withfluids such as DI water. In the various examples, several methods andapparatus are disclosed that assist in achieving high precision andcontrolled preparation. For instance, the preparation achieved by way ofthe systems and apparatus enable controlled scrubbing, buffing, andpolishing on desired surface locations of the substrate. That is, thesubstrate can be moved to different controlled locations within anenclosure to enable preparation at different surface locations and atdifferent times. The preparation, by way of the disclosed apparatus, canalso include contact with different preparation members (e.g., brushes,pads, etc.). Accordingly, the following description should be read inlight of the many alternatives described herein.

Wafer preparation apparatus: FIGS. 1 and 2 are a front endcross-sectional view and a right side cross-sectional view,respectively, of a wafer preparation apparatus in accordance with oneembodiment of the invention. As shown therein, wafer preparationapparatus 1 includes housing 2, which serves as a support structure forvarious components of the apparatus, as will be explained in more detailbelow. Semiconductor wafer W, which is shown edge-on in FIG. 1 andface-on (in phantom) in FIG. 2, is disposed on wafer drive rollers 6, 6′in a vertical orientation.

As shown in FIG. 1, wafer W is in contact with upper pair of polishingpads 8, 8′, with right pad 8 contacting right wafer face W1 and left pad8′ contacting left wafer face W2. Lower polishing pads 12, 12′ aredisengaged from right and left wafer faces W1, W2, respectively. Waferpreparation apparatus 1 need not be bilaterally symmetrical; however,numerous assemblies and sub-assemblies are preferably disposedsymmetrically in pairs to the right and left of the plane of symmetry ofwafer W as supported in a vertical orientation within housing 2. Forthat reason the terms “right” and “left” will generally be used hereinwith reference to wafer W as shown in FIG. 1. Alternatively, it ispossible to have a pair of brushes 12 b as well as a pair of pads asshown in FIGS. 11A and 11B. In the example, the brushes are identifiedas brushes 12 b and can either be mounted on a mandrel or a brush corethat is connected directly to one of the gears 44 or 46.

As shown in FIGS. 1-3, upper polishing pads 8, 8′ are mounted about theperimeter of cylindrical upper mandrels 10, 10′, and the lower polishingpads 12, 12′ are mounted about the perimeter of cylindrical lowermandrels 14, 14′. The upper and lower mandrels, which are disposedhorizontally, are arranged so that upper mandrel 10 and lower mandrel 14are on the right side of wafer W and upper mandrel 10′ and lower mandrel14′ are on the left side of wafer W. A selectable vertical spacingseparates upper and lower mandrel pairs 10, 10′ and 14, 14′,respectively. In one embodiment, the upper and lower pairs are spacedapart by a fraction of the wafer radius, preferably from aboutone-quarter to about three-quarters of the wafer radius. One end of eachof upper mandrels 10, 10′ and each of lower mandrels 14, 14′ isrotatably mounted within drive casings 16, 16′, each of which enclosesgearing that is rotatably coupled to wafer preparation drive assembly17. Additional details of wafer preparation drive assembly 17 are setforth below under the heading “Wafer Preparation Drive Assembly.” In oneembodiment, wafer preparation drive assembly 17 includes both padrotating mechanism 13 to transmit rotational torque to mandrels 10, 10′and 14, 14′ and pad engagement mechanism 15, which controllably movespolishing pads 8, 8′ and 12, 12′ into and out of contact with wafer W.

With reference to FIG. 1, right and left drive casings 16, 16′ pivotaround pivot points 18, 18′, each of which is located a small distancefrom the plane of the wafer W. When right drive casing 16 pivots tobring its upper end inward toward the plane of wafer W, upper polishingpad 8, which is mounted on mandrel 10, is moved into contact with rightwafer face W1 and the lower polishing pad 12, which is mounted onmandrel 14, is moved away from right wafer face W1. On the other hand,when right drive casing 16 pivots to bring its lower end inward towardthe plane of wafer W (see FIG. 3), lower polishing pad 12 is moved intocontact with right wafer face W1 and upper polishing pad 8 is moved awayfrom right wafer face W1. It will be apparent to those skilled in theart the foregoing description also applies to left drive casing 16′,which may pivoted to move upper and lower polishing pads 8′, 12′,respectively, into contact with left wafer face W2.

Thus, pivot points 18, 18′ are close enough to the plane of wafer W sothat drive casings 16, 16′ need only be pivoted through a moderate angleA, A′ to bring upper polishing pads 8, 8′ (or lower pads 12, 12′ for theopposite pivot angle) into contact with wafer faces W1, W2 so that waferW is “pinched” by the opposing polishing pads. The angle A depends on,among other things, the pad diameter. In one embodiment, the angle A isabout 15° to about 25°. However, as shown in FIG. 3, pivot points 18,18′ are far enough from the plane of wafer W so that when drive casings16, 16′ are pivoted to a generally vertical position, both upper pads 8,8′ and lower pads 12, 12′ assume a neutral position in which they aredisengaged and out of contact with wafer W by a substantial separation.

The pivoting action of drive casings 16, 16′ permits either the uppermandrel or the lower mandrel of each pair of mandrels to be separatelypressed inward so that the polishing pad mounted thereon contacts one ofthe wafer surfaces. As such, a wafer may be subjected to two separatepolishing operations within the wafer preparation apparatus: onepolishing operation with the wafer “pinched” between the upper polishingpads and the other polishing operation with the wafer “pinched” betweenthe lower polishing pads.

With continuing reference to FIGS. 1-3, wafer W is simultaneouslysupported and driven in rotation by wafer drive assembly 23. In oneembodiment, wafer drive assembly 23 is a variable height edge driveassembly. FIG. 2 shows wafer W (in phantom) in both a raised position,Wa, and a lowered position, Wb. As stated above, wafer drive rollers 6,6′ support wafer W. In FIG. 2, wafer drive rollers 6, 6′ are shown (inphantom) in corresponding raised positions 6 a, 6 a′ and loweredpositions 6 b, 6 b′. Wafer drive rollers 6, 6′ engage the waferperimeter edge, Wp, and are mounted to the end of roller arms 20, 20′,which in turn are pivotally mounted to a frame member. The frame membermay be supported on a suitable support structure, e.g., right side wall4 of housing 2 or housing floor 5.

Variable height edge drive assembly 23 includes roller drive mechanism21 to transmit rotational power to the drive rollers 6, 6′. Variableheight edge drive assembly 23 also includes wafer translation mechanism27 that regulates the pivotal movement of roller arms 20, 20′ bypivoting the arms about pivot points 22, 22′. Roller arms 20, 20′ aregeared together as a pair to cause them to counter-pivot insymmetrically opposed motion. Additional details of variable height edgedrive assembly 23, including additional details of roller drivemechanism 21 and wafer translation mechanism 27, are set forth belowunder the heading “Variable Height Edge Drive Assembly.”

Wafer top alignment roller 24 is mounted on alignment arm 25, which isin turn pivotally mounted to alignment tensioner 26 mounted to the upperportion of right side wall 4. Alignment roller 24 engages the waferperimeter edge, Wp, near the top of the wafer W, and serves both tomaintain alignment of wafer W and also to provide lateral support whenthe polishing pads (8, 8′, 12, 12′) are disengaged, i.e., in the neutralposition. The pivotal movement of alignment arm 25 permits top roller 24to remain engaged and to follow the wafer perimeter, Wp, as the wafermoves upward and downward as indicated by positions Wa and Wb (see FIG.2). In FIG. 2, the upper position of the top roller is shown as 24 andthe lower position is shown (in phantom) as 24′. If desired, additionaledge rollers may be used to assist in supporting, stabilizing, rotating,or loading/unloading the wafer.

Roller arms 20, 20′ and drive rollers 6, 6′ are shown in FIG. 2 in anintermediate angular position. A typical operational range of pivotalmovement of roller arms 20, 20′ is indicated by the upper and lowerdepictions of drive rollers 6, 6′ in phantom lines, which define thepivotal range of motion as angle B. The upward motion of the roller arms20, 20′ causes drive rollers 6, 6′ to move upward and closer together asa pair. This in turn causes wafer W to move upward, primarily because ofthe higher position of the drive rollers but also in part because thedrive rollers are spaced closer together. On the other hand, downwardpivoting of roller arms 20, 20′ causes a corresponding lowering of waferW. The movement of drive rollers 6, 6′ through angle B causes the wafercenter Wo to move up or down by a corresponding vertical travel distanceindicated by double-headed arrow C (see FIG. 2). The motion of driverollers 6, 6′ may be controlled to control the vertical motion of thewafer. By way of example, the drive rollers may be pivoted inwardly andoutwardly so that wafer W oscillates up and down relative to thepolishing pads (8, 8′ or 12,12′).

As shown in FIGS. 1-3, wafer W is disposed in a substantially verticalorientation and the polishing pads are disposed in a substantiallyhorizontal orientation. It will be apparent to those skilled in the artthat wafer W may be disposed in different orientations, if desired. Itwill be further apparent to those skilled in the art that the polishingpads may be disposed at an angle with respect to vertical, if desired.In this case, the motion of the wafer with respect to the pads shouldstill be generally perpendicular to the axis of the mandrels. Asubstantially vertical orientation of wafer W is preferred because itsimplifies the various support and drive assemblies in the apparatus andfacilitates the draining of polishing slurry, treatment solutions, andrinse solutions away from the polishing pads and the wafer.

Wafer preparation drive assembly: wafer preparation drive assembly 17 isshown in FIGS. 2 (cross-sectional view); 4A and 4B (elevational view asseen from outside end wall 3), and 5 (detailed cross-sectional view ofdrive casing and mandrel shown in FIG. 2). As shown in FIG. 2, drivecasing 16 connects to dual coaxial shaft assembly 19 that extendsthrough end wall 3. Coaxial shaft assembly 19 delivers both rotationalpower to the mandrels for wafer preparation via an inner shaft anddelivers pivotal activation and control to the drive casing forengagement/disengagement of the pads with the wafer faces via an outershaft. Thus, coaxial shaft assembly 19 is an integrated component ofboth pad rotating mechanism 13 and pad engagement mechanism 15. In oneembodiment, wafer preparation drive assembly 17 includes separatecoaxial shaft arrangements 19, 19′ for drive casings 16, 16′,respectively. The description herein with respect to the movement ofright drive casing 16 is also applicable to left drive casing 16′.

Coaxial shaft assembly 19 includes inner transfer shaft 28 and hollowouter pivot shaft 30. Transfer shaft 28 transmits rotational power tothe mandrels (10, 10′, 14, 14′) and is journaled to bearings 43 a and 43b, which are mounted on the inside of outer pivot shaft 30 adjacent toeach end thereof. Outer pivot shaft 30 is in turn journaled to waferpreparation drive assembly mounting frame 32 by bearings 31 a and 31 band provides pivoting control of drive casings 16, 16′ so that one ofthe pairs of the polishing pads (8, 8′ or 12, 12′) may be brought intocontact with wafer W.

As shown in FIGS. 2 and 4A, pad rotating mechanism 13 includes left andright wafer preparation motors 34, 34′, drive pulleys 36, 36′, belts 38,38′, and shaft pulleys 40, 40′. Drive pulleys 36, 36′ are rotatablymounted on motors 34, 34′, respectively, which are mounted beneath frame32. Belts 38, 38′ are disposed on drive pulleys 36, 36′ and shaftpulleys 40, 40′, which are mounted on the ends of transfer shafts 28,28′, respectively, that extend outside of frame 32. As shown in FIGS. 2and 5, transfer shaft 28 extends through end wall 3 to connect rigidlyto transfer pinion gear 42. Transfer shaft 28 is journaled by shaftbearing 43 a, which is in turn mounted within drive casing 16 inalignment with pivot point 18. Transfer shaft 28′ (not shown in FIGS. 2and 5) is connected and journaled in the same manner described fortransfer shaft 28.

As shown in detail in FIG. 5A, the inner portions of transfer shaft 28and pivot shaft 30 extend through end wall 3. Transfer pinion gear 42engages upper and lower mandrel gears 44 and 46, which are fixedlymounted to the end of upper and lower mandrels 10 and 14 (see FIGS. 1and 2), respectively, so as to be aligned with the mandrel axis. It isnoted that lower mandrel 14 shown in FIGS. 1 and 2 has been omitted fromFIG. 5A in favor of brush core 12 a and brush 12 b in accordance with analternative embodiment, as will be explained in more detail below. Thus,transfer gear 42 and mandrel gears 44 and 46 transmit torque to themandrel bodies so that both upper and lower mandrels 10 and 14 rotate inthe same direction simultaneously.

Upper and lower mandrels 10 and 14, respectively, may be rotatablymounted by conventional journal bearings to drive casing 16 so as to bedriven by mandrel gears 44, 46 while at the same time being supportedparallel to the face of wafer W. In one embodiment, mandrels 10 and 14are supported by self-aligning mandrel assembly 48 that automaticallyaligns polishing pads 8, 12 with the face of wafer W upon contact withthe wafer face so as to distribute the contact pressure of the padsevenly upon the surface of wafer W. Additional details of self-aligningmandrel assembly 48 are set forth below under the heading “Self-AligningMandrel Assembly.”

With reference to FIG. 4A, wafer preparation drive assembly 17 includesseparate drive motors 34, 34′ for drive casings 16, 16′. Motors 34, 34′may be operated by conventional power supplies, controls, and feedbacksensors (not shown) to rotate in opposite directions so that the pads(either 8, 8′ or 12, 12′) on opposite sides of wafer W are likewisecounter-rotating, preferably at substantially the same rotational rate.The rotation of the pads is preferably selected so that the pads exert adownward frictional force on the wafer and thereby helps to maintainwafer engagement with wafer drive rollers 6, 6′. Motors 34, 34′ may bemanually controlled or may be sequenced and controlled by a suitablyprogrammed computer system that activates conventional motor controllers(not shown). It will be apparent to those skilled in the art that, ifdesired, a single motor may be used with a suitable power transmission,such as a belt or gear transmission, to provide rotational power to bothdrive casings.

Pad engagement mechanism 15 controls the pivoting action of drivecasings 16, 16′ to bring either upper polishing pads 8, 8′ or lowerpolishing pads 12, 12′ into contact with the opposing faces of wafer W.As shown in FIG. 4A, outer pivot shafts 30, 30′ have levers 52, 52′mounted thereon such that each lever is directed generally inward towardthe wafer plane of symmetry, Wp. The end portion of each of levers 52,52′ is formed as a gear segment, and gear segments 54, 54′ have the sameradius and are concentric with outer pivot shafts 30, 30′, respectively.Gear segments 54, 54′ are intermeshed so that levers 52, 52′ and pivotsshafts 30, 30′ coupled thereto are slaved together to pivot in acoordinated manner in opposite directions.

Linear actuator 56, which may be a conventional air cylinder or otherequivalent actuator, is mounted to the lower portion of frame 32 (seeFIGS. 2 and 4A), with actuator output rod 58 extending upward to pivotalconnection 59 adjacent to the end portion of lever 52 (see FIGS. 4A and4B). Thus, an upward extension of rod 58 causes lever 52 to pivotcounter-clockwise (from the perspective of FIG. 4A) and causes oppositelever 52′ to pivot clockwise through an equal angle via enmeshed gearsegments 54, 54′. As shown in FIG. 4B, rod 58 is extended upward(relative to the position shown in FIG. 4A) to pivot the levers 52, 52′in the manner just described. Those skilled in the art will recognizethat a downward retraction of rod 58 (not shown) produces a pivotingaction opposite to that shown in FIG. 4B. In other words, when rod 58 isretracted downwardly, lever 52 pivots clockwise and lever 52′ pivotscounter-clockwise.

As shown in FIGS. 2 and 5A, outer pivot shaft 30 is rigidly connected todrive casing 16 so that any rotation of pivot shaft 30 causes a likerotation of the drive casing. The rotation of drive casing 16 in turncauses a corresponding movement of the upper and lower mandrels 10 and14 (or brushes 12 a/12 b), respectively, toward or away from the planeof wafer W. The range of throw of actuator rod 58 is preferably selectedand controlled to provide a pivoting range of outer pivot shafts 30, 30′sufficient to permit selective engagement of upper and lower polishingpads 8 and 12, respectively, with wafer W. As noted above, the pivotingrange will depend on, among other things, the diameter of the polishingpads. The motion of linear actuator 56 may be manually controlled byconventional actuator controls and power supplies (not shown) or,alternatively, may be sequenced and controlled by a suitably programmedcomputer system that activates conventional controllers (not shown). Ifdesired, conventional feedback sensors or load regulators may beincluded to control the force applied by linear actuator 56 via waferpreparation drive assembly 17 so that one or both of the contact forceand surface pressure of the polishing pads on wafer W may be controlled.

It will be apparent to those skilled in the art that alternative powertransmission systems may be used to provide rotational and pivotal powerand control to drive casings 16, 16′. It also will be apparent to thoseskilled in the art that alternative configurations of drive casings 16,16′ and wafer preparation drive assembly 17 may be used. For example,drive motors may be mounted directly to drive casings 16, 16′ to providerotational power to polishing pads 8, 8′ and 12, 12′ without the use ofa coaxial shaft. Further, drive casings 16, 16′ may be moved toward oraway from the wafer with a linear motion rather than a pivotal motionby, for example, mounting the drive casings to a telescoping linearactuator directed toward one of the opposing wafer faces.

Variable Height Edge Drive Assembly: variable height edge drive assembly23 includes coaxial shaft assembly 61 as a component of both rollerdrive mechanism 21 and wafer translation mechanism 27 (see FIGS. 1 and2). Coaxial shaft assembly 61 delivers both rotational power to waferdrive rollers 6, 6′ for wafer rotation and also pivotal activation andcontrol to roller arms 20, 20′ for adjusting the vertical position ofwafer W with respect to polishing pads 8, 8′ and 12, 12′. Variableheight edge drive assembly 23 includes separate coaxial shaft assemblies61, 61′ for front and rear roller arms 20, 20′, respectively. Thedescription herein regarding the structure and operation of coaxialshaft assembly 61 and front roller arm 20 therefore generally applies tothe structure and operation of coaxial shaft assembly 61′ and rearroller arm 20′.

As shown in FIG. 1, coaxial shaft arrangement 61 includes inner transfershaft 60 and hollow, outer, roller pivot shaft 62. Transfer shaft 60 isan element of roller drive mechanism 21, and transmits rotational powerto roller 6 via transfer belt 64. Transfer shaft 60 is journaled tobearings 63 a and 63 b, which are mounted on the inside of roller pivotshaft 62 adjacent to each end of the shaft. Roller pivot shaft 62 is inturn journaled to a support structure, e.g., right wall 4, by bearings65 a and 65 b. Roller pivot shaft 62 provides pivoting control of rollerarm 20 so as to move roller 6 between an upward/inward position 6 a anda lower/outward position 6 b, as shown in FIG. 2.

As shown in FIGS. 1 and 2, roller drive mechanism 21 includes left andright roller motors 66, 66′, respectively, which are mounted to thelower portion of right wall 4. Motors 66, 66′ are rotatably coupled todrive pulleys 68, 68′, respectively, which engage drive belts 70, 70′.Outer transfer shaft pulleys 72, 72′, which are mounted to the ends oftransfer shafts 60, 60′, respectively, that extend through right wall 4,also engage drive belts 70, 70′.

With reference to FIG. 1, the end of transfer shaft 60 that extendsthrough right wall 4 is rigidly mounted to inner transfer pulley 74within roller arm casing 76 so as to be in alignment with roller armpivot point 22. Inner pulley 74 engages roller transfer belt 64, whichextends within roller arm casing 76 to engage roller pulley 78. Rollerpulley 78 is mounted to the end of roller shaft 80 journaled adjacent tothe outer end of roller arm casing 76. Roller shaft 80 in turn extendsthrough roller arm casing 76 toward the plane of wafer W to supportwafer drive roller 6 outside of the casing.

In one embodiment, roller drive mechanism 21 includes separate drivemotor 66, 66′ for each of roller drive arms 20, 20′, as shown in FIG. 2.Motors 66, 66′ may be operated by conventional power supplies, controls,and feedback sensors (not shown) to rotate in the same direction so thatwafer drive rollers 6, 6′ rotate in the same direction at substantiallyequal rotational rates. Motors 66, 66′ may be manually controlled or maybe sequenced and controlled by a suitably programmed computer systemthat activates conventional motor controllers (not shown). In anotherembodiment, a single motor is used with suitable power transmission,such as a belt or gear transmission, to provide rotational power to bothroller drive arms.

As shown in FIGS. 1-3, wafer translation mechanism 27, which providespivotal actuation and control of roller drive arms 6, 6′, includes rightand left roller pivot shafts 62, 62′, respectively (left roller pivotshaft 62′ is not shown in FIGS. 1-3), each of which extends a distancebeyond, i.e., outside, right wall 4. The outer end of each roller pivotshaft 62, 62′ is surrounded by and fixed to one of a pair of co-planargear rings 82, 82′, the effective outer diameter of each of the gearrings preferably being one-half the span between roller arm pivot points22, 22′, so that the front and rear gear rings 82, 82′, respectively,intermesh at the approximate mid-span. Intermeshed gear rings 82, 82′cause the respective roller pivot shafts 62, 62′ to be slaved togetherto pivot in a coordinated manner in opposite directions. Roller pivotshafts 62, 62′ are rigidly connected to roller arm casings 76, 76′,respectively, so that any pivoting motion of the shafts produces a likepivoting motion of roller drive arms 20, 20′ and wafer drive rollers6,6′.

As shown in FIG. 2, linear actuator 84, which may be a linear steppermotor or other equivalent actuator, is mounted generally horizontally tothe lower outside portion of right wall 4. Actuator output rod 86extends laterally to pivotal connection 87 adjacent the end portion ofactuator lever 88. Actuator lever 88 is in turn fixed to the side of oneof the gear rings 82, 82′. An outward extension of rod 86 causes lever88, gear ring 82 (or 82′), and roller pivot shaft 62 to pivotcounter-clockwise (from the perspective of FIG. 2), which in turn causesopposite enmeshed gear ring 82′ (or 82) and pivot shaft 62′ to pivotclockwise through an equal angle. This pivoting action moves wafer driverollers 6, 6′ toward their lower, outward positions 6 b, 6 b′. An inwardretraction of rod 86 produces a corresponding opposite pivoting actionthat moves wafer drive rollers 6, 6′ toward their upper, inwardpositions 6 a, 6 a′.

The range of throw of actuator rod 86 is preferably selected andcontrolled to provide a pivoting range of shafts 62, 62′ sufficient tomove wafer W through a preselected vertical range, as indicated by arrowC (see FIG. 2). This preselected vertical range is formulated to bringthe desired portions of the wafer in position to engage polishing pads8, 8′ or 12, 12′, as will be explained in more detail later. Thediameter of wafer drive rollers 6, 6′ and the length of roller drivearms 20, 20′ may be preselected to accommodate a predetermined range ofwafer diameters, e.g., 200 mm wafers and 300 mm wafers. If desired,substitute roller drive arm casings 76, 76′, roller transfer belts 64,64′, and wafer drive rollers 6, 6′ may be provided in a range of sizesfor convenient installation to permit the geometry of roller drivemechanism 21 to be adjusted to suit an even broader range of waferdiameters. In this same vein, substitute actuator levers 88 may beprovided in a range of lengths (or lever 88 may be mechanicallyadjustable in length) to adjust the mechanical advantage of linearactuator 84. The motion of linear actuator 84 may be manually controlledby conventional actuator controls and power supplies (not shown) or,alternatively, may be sequenced and controlled by a suitably programmedcomputer system that activates conventional controllers (not shown).

It will be apparent to those skilled in the art that alternative powertransmission systems may be used to provide rotational and pivotal powerand control to wafer drive rollers 6, 6′ and roller drive arms 20, 20′.It also will be apparent to those skilled in the art that theconfiguration of the variable height edge drive assembly be varied fromthat shown herein. For example, an alternative variable height edgedrive assembly may include non-pivoting wafer drive rollers andassociated motors mounted to a variable height support platform.

Self-aligning mandrel assembly: as shown in FIG. 5A, upper mandrel 10,to which polishing pad 8 is affixed, is supported by self-aligningmandrel assembly 48. Mandrel assembly 48 includes rigid, cylindrical,rod-like spine 90, which is rigidly connected to wafer preparation drivecasing 16 so as to provide a cantilevered support for mandrel 10. Spine90 extends generally parallel to wafer W and terminates at point beyondmandrel centerline 91. Upper mandrel gear 44, which has a hollow core,surrounds spine 90 and is journaled upon the spine by gear bearing 92,so that the mandrel gear may rotate independently of the fixed spine(spine 90 is fixed relative to drive casing 16). Upper mandrel gear 44connects to mandrel core 94 so as to transmit rotational torque thereto.Mandrel core 94, which is formed as a hollow cylinder and surroundsspine 90 with clearance, is journaled on core bearing 96 adjacentmandrel centerline 91 so that the core may rotate independent of thespine when driven by mandrel gear 44. Seals 97 a and 97 b are situatedon the outside and inside of the hollow shaft 98 of mandrel gear 44. Theseals 97 a and 97 b are configured to keep fluids and/or slurry out ofthe drive casings 16.

Mandrel shell 100, which is formed as a hollow cylinder and extends atleast the desired length of polishing pad 8, surrounds mandrel core 94with clearance. Mandrel shell 100 is supported by shell center fulcrum102 at a point adjacent to mandrel centerline 91. Shell center fulcrum102 may be any suitable structure that surrounds core 94. In oneembodiment, shell center fulcrum 102 is a resilient O-ring disposed ingroove 104 formed in the outer surface of mandrel core 94. Shell centerfulcrum 102 provides a center support for mandrel shell 100 whilepermitting the shell to tilt through a small angle away from parallel tocore 94. The clearance between mandrel core 94 and mandrel shell 100 isselected to permit the shell to tilt through a predetermined tilt range.Polishing pad 8 is affixed to the outer surface of mandrel shell 100. Inone embodiment, polishing pad 8 is spirally wrapped around mandrel shell100 such that the polishing pad is substantially symmetrically disposedabout mandrel centerline 91.

Torque connector 106 is mounted between mandrel core 94 and mandrelshell 100. The function of torque connector 106 is to transmitrotational torque from the core to the shell as well as to fix the shellwith respect to axial movement relative to the core, while stillpermitting the shell to tilt within the predetermined tilt range. In oneembodiment, torque connector 106 is a spring-loaded key structure set inaligned slots in mandrel core 94 and mandrel shell 100. In anotherembodiment, torque connector 106 is a drive pin.

As polishing pad 8 is pressed into contact with one of the surfaces ofwafer W (not shown in FIG. 5A) by the pivoting action of drive casing16, the contact pressure of the polishing pad with the wafer will causemandrel shell 100 to tilt until the polishing pad is aligned parallel toone of the wafer surfaces and the contact pressure is evenly distributedalong the line of contact. Torque connector 106 simultaneously transmitsrotational torque to mandrel shell 100 so that polishing pad 8 rotatesand thereby generates polishing action on the surface of the wafer.

FIG. 5B is a more detailed view of self-aligning mandrel assembly 48shown in FIG. 5A that focuses on the region proximate to shell centerfulcrum 102. As noted above, shell center fulcrum 102 is shown as anO-ring. In one embodiment, the O-ring has a durometer hardness of about70-80 on the Shore A scale. The O-ring is seated in groove 104 formed inmandrel core 94, which may be formed of plastic material. It will beapparent to those skilled in the art that spine 90 has been omitted fromFIG. 5B for ease of illustration. Groove 104 is located at thecenterline of mandrel shell 100, which may be formed of stainless steel.Torque connector 106, which is shown as a drive pin, is disposed incorresponding holes in mandrel shell 100 and mandrel core 94. As shownin FIG. 5B, the hole in mandrel shell 100 is oversized for the drive pinso that the mandrel shell is free to pivot about the O-ring, asdescribed above. In one embodiment, the ends of mandrel shell 100 canmove up to about ±0.060 inch. Polishing pad material 8 is spirallywrapped around mandrel shell 100 such that there is a slight gap betweenthe wrap. This configuration avoids any overlap of the polishing padmaterial, which may adversely affect the polishing operation. In oneembodiment, the polishing pad material is polyurethane foam.

Fluid injection: as shown in FIG. 1, a plurality of nozzles 110 aremounted to the walls of housing 2. Nozzles 110 are directed to sprayfluids toward the opposing faces of wafer W or polishing pads 8, 8′ and12, 12′. Suitable fluids, which are supplied to nozzles 110 by manifolds112, include abrasive slurries, chemical treatment solutions, emulsions,cleaning solutions, rinse solutions, coolant solutions, deionized (DI)water, and mixtures thereof. If desired, different fluids may beinjected simultaneously from different nozzles or may be injected insequence from the same or different nozzles. Drain 114 in sloped floor 5is provided to facilitate removal of spent fluids from the interior ofhousing 2. Additional nozzles and manifolds may be located withinhousing 2 to rinse slurries or solutions from wafer preparation memberssuch as polishing pads and brushes as well as from support componentssuch as mandrels, drive casings, rollers, and roller arms uponcompletion of one or more wafer preparation operations. The fluids maybe supplied to manifolds 112 by conventional conduits, valves, pumps,storage tanks, filters, and sumps (not shown) coupled in flowcommunication with the manifolds. The sequence and rate of fluidinjection may be manually controlled or, alternatively, may beautomatically controlled by a suitably programmed computer that operatesconventional valves, pumps, and actuators.

Pad Conditioners: as shown in FIGS. 1 and 3, optional retractable padconditioners 116 are pivotally mounted to the inside walls of housing 2adjacent to each polishing pad. Each conditioner 116,includes generallyhorizontal blade 118 that spans substantially the entire length of thepolishing pad disposed proximate thereto. Each blade 118 is pivoted atpivot 120 above the blade, so that the blade may be extended toward theadjacent polishing pad by impingement of actuator 122. Actuator 122 maybe a conventional solenoid actuator mounted to impinge an output rod 124against the outer portion of blade 118, thereby causing the blade topivot inward through angle D. Pad drive casings 16, 16′ may besimultaneously moved through angle E (pad 8) or angle E′ (pad 10) tobring the respective polishing pads into contact with the correspondingblade 118 for conditioning. Angles D and E and the conditionerdimensions are preferably selected so that each of the polishing pads 8and 10 may be conditioned without either pad contacting the surface ofwafer W. In other words, pad conditioning preferably takes place withthe polishing pads in the neutral” position so that the wafer need notbe removed for pad conditioning. Upon completion of a pad conditioningoperation, each of blades 118 may be retracted by deactivating actuators122.

FIG. 10 shows a three-dimensional diagram of a wafer preparation station200 in accordance with one embodiment of the invention. The waferpreparation station 200 includes a housing 2 which is configured toenclose a wafer preparation apparatus 210. A top portion of the housing2 includes an opening 204 through which the wafer can be lifted out andplaced into another processing station, if desired. Alternatively, theopening 204 can be omitted leaving a fully-enclosed wafer preparationapparatus 210. The housing 2 also includes a door 202 which isconfigured to allow access to the wafer preparation apparatus formaintenance, such as to replace or insert scrub brushes or polishingpads and associated mandrels.

During operation, the door 202 is preferably closed to preserve thecleanliness of the environment and to reduce the exposure toparticulates and debris. In one preferred embodiment, a slot 206 isprovided in the door 202 to enable the wafer W to be inserted into thewafer preparation station 200. In the same manner, the wafer can beremoved from the wafer preparation station through the slot 206. Instill a further embodiment, the door 202 can include a slider door (notshown), which will close the slot 206 when the wafer is being processed.

As an overview, the wafer preparation apparatus 210 includes mandrels 10and 14 which are provided with pads 8. In this implementation, both setsof mandrels 10 and 14 are provided with the pads 8 to facilitate buffingor polishing of the wafer by either the lower set of mandrels or theupper set of mandrels when desired. As mentioned above, the wafer isconfigured to be raised and lowered during preparation, and the firstset of mandrels or the second set of mandrels can be positioned toachieve the aforementioned off-center processing. Also shown are thenozzles 110, which can be configured to direct fluids onto the pads 108.The nozzles 110 can be coupled in flow communication with an appropriatesource to provide DI water, chemicals, or slurry, depending upon theprocess being performed. The wafer preparation apparatus 210 is alsoshown including the alignment tensioner 26 which, as described above, isconfigured to apply the wafer top alignment roller 24 to a top edge ofthe wafer. This illustration also shows a linear actuator 84 (which ispreferably a linear stepper motor), that is used to cause the wafer tobe raised or lowered in accordance with a wafer movement scheduleformulated to achieve a desired wafer material removal rate at variousradial locations on the wafer surface. The linear actuator 84 is shownin greater detail in FIG. 11A. Also shown is the roller drive mechanism21, which is designed to cause the rotation of each of the wafer driverollers 6.

FIG. 11A illustrates in greater detail the wafer preparation apparatus210. The wafer preparation apparatus 210 is generally configured toinclude a first pair and a second pair of wafer preparation assemblies212. Each of the wafer preparation assemblies 212 will reside on aparticular side of the wafer W. For example, the wafer preparationassembly 212 is shown to include a mandrel 10 and a brush 12 b connectedto a drive casing 16. On the opposite side of the wafer, another waferpreparation assembly 212 is provided, also including a mandrel 10 forthe bottom part of the assembly and a brush 12 b for the top part of theassembly.

This illustration is provided to make clear that the wafer preparationapparatus 210 can be configured in many ways. For example, each of thewafer preparation assemblies 212 can be configured to include mandrelsthat have polishing pads 8 affixed thereto as shown in FIG. 10. In theillustrated embodiment of FIGS. 11A and 11B, the bottom part of thewafer preparation assembly 212 is a mandrel 10 and the top part is abrush 12 b. In the case of brush 12 b, the mandrel is replaced with astandard brush core 12 a which connects to the drive casing 16. In oneembodiment, the brushes 12 b can be polyvinyl alcohol (PVA) brushes. ThePVA brush material is configured to be soft enough to prevent damage tothe wafer's delicate surface, yet can provide good mechanical contactwith the wafer surface to dislodge residues, chemicals and particulates.Exemplary cleaning systems that implement PVA brushes include thosedescribed in U.S. Pat. No. 5,875,507, which is incorporated herein byreference. Further, a standard brush core 12 a can, in one embodiment,be configured to deliver fluids through the brush (TTB).

As mentioned above, linear actuator 84 is configured to have an actuatoroutput rod 86, which connects to an actuator lever 88. The combinationof the linear actuator 84, the actuator output rod 86, and the actuatorlever 88 is configured to assist in moving the roller arms 20 in anupward or downward direction to enable movement of the wafer W up ordown, depending on the location (i.e., on-center or off-center) desiredfor buffing, polishing, or scrubbing. The motors 66 are configured tocause the rotation of the wafer drive rollers 6 by way of the rollerarms 20 as shown in FIG. 11B.

Still referring to FIG. 11A, a wafer preparation drive assembly 17 isprovided to provide a connection and support location for each of thewafer preparation assemblies 212. As shown, the wafer preparation driveassembly 17 includes a frame 32. The frame 32 provides support for apair of outer pivot shafts 30. Each of the outer pivot shafts 30connects to one of the wafer preparation assemblies 212 through theframe 32. Each of the outer pivot shafts 30 also includes an innertransfer shaft 28. The belts 38 link together the transfer shaft pulley40 and the drive pulley 36, thus causing a rotation by way of waferpreparation drive motor 34. The rotation of the transfer shaft pulley 40thus causes the rotation of the inner transfer shaft 28 that transfersthat rotation to the drive casing 16. The rotation of the inner transfershaft 28 is therefore transferred to each of the mandrels 10 and brushes12 b.

By way of example, the rotation of the inner transfer shaft 28 willcause a rotation of gears within drive casing 16. The rotation of thegears within the drive casing 16 will cause the brush 12 b to rotate aswell as the mandrel 10. With regard to FIGS. 11A and 11B, the mandrel 10of each of the wafer preparation assemblies 212 will contact the wafer Wat the same time from both sides of the wafer while the brushes 12 b arespaced apart from the wafer. In the same manner, the drive casing 16 canbe tilted in the opposite direction so that only the brushes 12 b of thewafer preparation assemblies are contacting the wafer on each side. Inthis situation, the mandrels 10 will be spaced apart from the wafer,thus allowing only brush scrubbing of the wafer surfaces. The mechanismconfigured to pivot the drive casings 16 so that only one of either themandrel 10 or the brush 12 b is in contact with a surface of the waferis shown and described in greater detail above.

Methods of wafer preparation: one of the methods of wafer preparationprovided by the present invention is an off-diameter polishing methodthat produces an overall more radially uniform removal of wafer materialduring a polishing operation relative to conventional centerlinepolishing. Before polishing, a wafer may be planarized using aconventional planarization technique, e.g., CMP. In one embodiment, theoff-diameter polishing produces a polished surface without producingsubstantial departures from the initial planar surface. FIGS. 6-9 showexamples of both centerline (on-diameter) polishing and off-diameterpolishing.

FIG. 6 is a graph of the amount of wafer material removed versus radiallocation across the wafer face for four samples of centerline polishingas in the prior art. The amount of wafer material removed is plotted onthe vertical axis (in angstroms (10⁻¹⁰ m)) and the radial location ofthe test point is plotted on the horizontal axis (121 evenly spacedpoints across the wafer diameter, with a 5 mm edge exclusion). As shownin FIG. 6, centerline polishing in which the line of contact of the padcrosses the wafer center typically results in significantly more wafermaterial being removed from the center region of the wafer than isremoved from the peripheral regions of the wafer.

In circumferential polishing operations, the rotational speed of thepolishing pads is typically higher than that of the wafer. The polishingpads push on each side of the wafer, preferably with equal pressure oneach side, as they counter-rotate inward toward the nip, with the padsurface rotation at the line of contact being oriented downwardly. Theabsolute amount of wafer material removed at a particular point is afunction of factors such as polishing time, pad contact pressure, padcomposition, pad rotational rate, wafer rotational rate, and abrasiveslurry composition. Nevertheless, the relative amount of wafer materialremoved in a typical centerline polishing operation may be an order ofmagnitude greater near the center of the wafer, as demonstrated by thepronounced peak in the amount of substrate material removed betweenpoints 50 and 70 in FIG. 6. The wafer contour produced by suchcenterline polishing is the inverse of the curve shown in FIG. 6. Inother words, the high wafer material removal rate near the wafer centerproduces a concave or “dished” contour near the wafer center. Thus, fora given set of polishing parameters, the wafer material removal rate ishighly non-uniform across the span of contact of the polishing pad withthe wafer.

FIGS. 7A and 7B demonstrate that the removal of wafer material incenterline polishing tends to be substantially radially symmetricalwithin a modest range of random variation. FIG. 7A shows 49 test pointlocations for four different samples of centerline polishing. FIG. 7B isa graph of the amount of substrate material removed (measured inangstoms greater or less than mean thickness change) at each point forthe four samples. As shown in FIG. 7A, the test points include the wafercenter (point 1), an evenly-spaced concentric ring at about one-third ofthe radius (points 2-9), a similar ring at about two-thirds of theradius (points 10-25), and a similar ring inset about 5 mm from thewafer perimeter (points 26-49). FIG. 7B is scaled so that the wafercenter (point 1) is off the plot, to allow greater detail and clarity inthe plot of points 2-49 because, as discussed of above, the amount ofsubstrate material removed near the center is an order of magnitudegreater than the amount removed over a majority of the wafer surface. Asshown in FIG. 7B, the amount of substrate material removed falls intothree distinct “steps,” which correspond to the three concentric ringsof test points. The variation within each step has a random characterand shows no systematic angular trend.

In the off-diameter polishing method of the invention, just as incenterline polishing, the absolute amount of substrate material removedat a particular point on the wafer surface is a function of the variousparameters set forth above in connection with the description of FIGS.6, 7A, and 7B. In off-diameter polishing in accordance with theinvention, however, the amount of substrate material removed also is afunction of the motion of the wafer relative to the line of contact ofthe polishing pads. Accordingly, the wafer preparation apparatus of theinvention enables the movement of the wafer relative to the waferpreparation members, e.g., polishing pads, to be controlled. Thisenables the amount of substrate material removed at various locationsacross the surfaces of the wafer to be controlled so that a planar orother desired contour is obtained.

A controlled wafer movement schedule may be formulated in which thewafer is moved either up or down relative to the polishing pads toobtain the desired contour for the wafer surfaces. At some point duringthe polishing operation, the pad line of contact must cross the wafercenter, i.e., the zero radial distance position, to ensure that theentire surface of the wafer is polished. It will be apparent to thoseskilled in the art that the wafer movement schedule may be formulated sothat the pad line of contact either starts at the wafer center and movestoward the edge of the wafer or starts at the edge of the wafer andmoves toward the wafer center.

Those skilled in the art will recognize that other polishing parameterssuch as, for example, the pad rotation rate, the wafer rotation rate,the pad bearing pressure, or a combination of these parameters also maybe controlled to obtain the desired amount of substrate material removalacross the wafer. The movement of the wafer relative to the polishingpads as well as the other polishing parameters may be controlled bysuitable software code read by a computer system that actuatesconventional control devices to govern the polishing operation. By wayof example, the control devices may govern the operation or one or moreof linear actuator 84 for moving the wafer up and down, drive rollermotors 66, 66′, linear actuator 56 for pivoting drive casings 16, 16′,and pad motors 34, 34′.

The off-diameter polishing method of the invention advantageouslycompensates for the radial variation in the rate of removal of substratematerial from the wafer surface by moving the wafer relative to thepolishing pads to obtain a polished wafer surface having a planar orother desired contour. By controlling the speed at which the wafer ismoved relative to the polishing pads (or by controlling other polishingparameters to achieve the same effect as controlling the wafer speed),desired substrate material removal rates may be obtained at differentradial locations on the wafer surfaces. If desired, the polishingparameters may be controlled to obtain a substantially uniform substratematerial removal rate across the wafer. This control regime may beparticularly useful for polishing wafers having planarized surfaces.Alternatively, the polishing parameters may be controlled to vary thesubstrate material removal rate across the wafer. This control regimemay be particularly useful for polishing wafers that have contoured,e.g., concave or convex, surfaces to obtain polished wafers havingsubstantially planarized surfaces.

The wafer material removal rate for a particular polishing regime can bereadily determined by analyzing test samples. For example, FIGS. 8A and8B show the rate of wafer material removal (in angstroms per minute or“A/m”) as a function of radial position for 200 mm diameter test waferspolished at centerline only in accordance with conventional practice.The test wafers were polished with the apparatus described herein usingan abrasive slurry and a pad rotation of 200 RPM. The wafer rotation wasvaried from 30 RPM (FIG. 8A) to 50 RPM (FIG. 8B). As shown in FIGS. 8Aand 8B, the wafer material removal rate undergoes a significantnon-linear increase near the center of the wafers (the center portion(approximately −5 to 5 mm) is not plotted for clarity of scale).

FIGS. 9A and 9B show the rate of wafer material removal (in A/m) as afunction of radial position for 200 mm diameter test wafers subjected tooff-diameter polishing in accordance with one embodiment of theinvention. The test wafers were polished under similar conditions tothose described above in connection with the description of FIGS. 8A and8B, except that the test wafers were moved at a constant rate relativeto the polishing pads (excluding the immediate center and edge region).In addition, the pad rotation was 600 RPM (for both test wafers) and thewafer rotation was 30 RPM (for both test wafers). The translation rate(the relative velocity of the wafer to the polishing pads) was variedfrom 10 inches per minute (ipm) (FIG. 9A) to 40 ipm (FIG. 9B).

The wafer material removal rate obtained using off-diameter polishing issignificantly more radially uniform than that obtained usingconventional centerline polishing (compare the curves shown in FIGS. 9Aand 9B with those shown in FIGS. 8A and 8B). As indicated by thesomewhat sloped curves shown in FIGS. 9A and 9B, however, off-diameterpolishing causes a slightly higher rate of wafer material removal tooccur toward the edge of the wafer. In addition, the faster translationrate, 40 ipm, resulted in a mean wafer material removal rate of about 90A/m (see FIG. 9B), whereas the slower translation rate, 10 ipm, resultedin a mean wafer material removal rate of about 120 A/m (see FIG. 9A).Thus, the faster translation rate resulted in a slightly lower wafermaterial rate than the slower translation rate. Nevertheless, given thata four-fold increase in translation rate caused only about a 25%reduction in the wafer material removal rate, it is believed that FIGS.9A and 9B demonstrate that the translation rate is not a dominant factorin determining the wafer material removal rate. Instead, it is believedthat the total amount of wafer material removed at any radial locationis predominantly a function of the total polishing exposure orequivalent dwell time.

In one embodiment, the length of the polishing pad is sufficient to spanthe entire wafer chord at all translation positions so that abruptdiscontinuities of pad contact are avoided. Thus, at any specific padposition during translation, the portion of the wafer surface outsidethe pad line of contact, i.e., the portion farther from the wafercenter, is exposed to polishing action. On the other hand, at the sametranslation position, the portion of the wafer surface inside the padline of contact, i.e., the portion nearer to the wafer center, is notexposed to polishing action. As shown in FIGS. 6-8, the wafer materialremoval rate is not necessarily uniform across the pad line of contact.

The off-diameter polishing method may be implemented by formulating asuitable wafer movement, i.e., translation schedule, which is apredetermined schedule of wafer position relative to the polishing padsversus time during a polishing operation. In one embodiment, theoff-diameter polishing method is implemented using a wafer movementschedule formulated to obtain substantially the same amount of wafermaterial removal at each radial location, i.e., radially uniformthickness reduction. In another embodiment, the off-diameter polishingmethod is implemented using a wafer movement schedule formulated toobtain different amounts of wafer material removal at certain radiallocations, i.e., radially variable thickness reduction.

In one embodiment of the off-diameter wafer preparation method of theinvention, each of the opposing surfaces of a vertically oriented waferis contacted with a cylindrical wafer preparation member so as to definea substantially linear contact area. As the wafer is rotated, at leastone wafer preparation parameter is controlled to obtain a variable wafermaterial removal rate as the contact areas on the wafer are moved from afirst position to a second position. In one embodiment, the variablewafer material removal rate is formulated to provide the wafer with asubstantially uniform thickness after processing. The wafer preparationparameter that is controlled may be one of the pressure applied to thewafer by the wafer preparation member, the rotational speed of thewafer, the rotational speed of the wafer preparation members, and aspeed at which the contact areas defined on the opposing surfaces of thewafer are moved from the first position to the second position.

In one embodiment, the first position is the wafer centerline and thesecond position is a distance from the centerline, e.g., proximate tothe edge of the wafer. The wafer may be raised or lowered to move thecontact areas from the first position to the second position. In oneembodiment, the rate at which the wafer is moved in a vertical directionto move the contact areas from the first position to the second positionis controlled such that the wafer has a substantially uniform thickness.By analyzing test wafers to determine the radial variation in wafermaterial removal rate for a given polishing regime, those skilled in theart can readily formulate a suitable wafer movement schedule to obtainprocessed wafers having a substantially uniform thickness.Alternatively, the wafer can be moved (either up or down) at a constantrate and one or more of the other polishing parameters, e.g., pressure,wafer rotational speed, and wafer preparation member rotational speed,can be controlled to obtain the same effect. Thus, the off-diameterwafer preparation method may be configured to process wafers havingslightly concave or convex surface contours into wafers havingsubstantially planar contours.

Another method provided by the present invention is a method forpreparing a semiconductor wafer in which two wafer preparationoperations are performed on a vertically oriented wafer in a singleenclosure. In this method a pair of wafer preparation assemblies, e.g.,wafer preparation assemblies 212 shown in FIG. 11A, are disposed in anopposing relationship in a suitable enclosure, e.g., a housing. Each ofthe wafer preparation assemblies includes a first wafer preparationmember and a second wafer preparation member. By way of example,suitable wafer preparation members include cylindrical polishing padsand cylindrical brushes. After being disposed between the opposing waferpreparation assemblies in a vertical orientation, the wafer is rotatedby a suitable wafer drive assembly.

To perform a first wafer preparation operation, the wafer preparationassemblies are oriented such that the first wafer preparation memberscontact opposing surfaces of the rotating wafer in an opposingrelationship. In one embodiment, the wafer preparation assemblies arepivoted in a first direction to bring the first wafer preparationmembers into contact with the opposing surfaces of the rotating wafer.Once the first wafer preparation operation is done, the waferpreparation assemblies are oriented such that the second waferpreparation members contact opposing surfaces of the rotating wafer inan opposing relationship. In one embodiment, the wafer preparationassemblies are pivoted in a second direction, which is opposite to thefirst direction, to bring the second wafer preparation members intocontact with the opposing surfaces of the rotating wafer.

The wafer preparation assemblies may be configured to perform anydesired combination of wafer preparation operations. In one embodiment,the first wafer preparation operation is a cleaning operation andtherefore each of the first wafer preparation members is a cylindricalbrush. In this embodiment, the second wafer preparation operation is apolishing operation and therefore each of the second wafer preparationmembers is a cylindrical polishing pad. If desired, the order of theseoperations may be reversed so that the first operation is a polishingoperation and the second operation is a cleaning operation.

In another embodiment, both the first and second wafer preparationoperations are cleaning operations. By way of example, the firstcleaning operation may be configured to remove relatively coarseparticles and the second cleaning operation may be configured to removerelatively fine particles. In yet another embodiment, both the first andsecond wafer preparation operations are polishing operations. By way ofexample, the first polishing operation may be configured to remove adesired amount of wafer material and the second polishing operation maybe configured to provide a desired surface finish.

If desired, the wafer may be moved in a vertical direction, i.e., up ordown, while in contact with either the first wafer preparation membersor the second wafer preparation members in accordance with theoff-diameter wafer preparation method of the invention. The wafer may bemoved in a vertical direction by a suitable variable height edge driveassembly. In one embodiment in which both the first and second waferpreparation operations are polishing operations, the wafer is moved in avertical direction during at least one of the polishing operations.

Once a wafer is processed in the apparatus and/or prepared using thedisclosed methods, the wafer can be processed through other well knownfabrication operations. These operations include, as is well known,deposition or sputtering of oxide materials and conductive materials(e.g., aluminum, copper, mixtures of aluminum and copper, and the like).The process, also known as “the backside” process also includes etchingoperations. These etching operations are designed to define the networkof metallization lines, vias, and other geometric patterns necessary todefine the interconnect structure of an integrated circuit device. Inbetween these operations, some chemical mechanical polishing (CMP)operations are also needed to planarize the surface to enable moreefficient fabrication. After any of such operations, the wafer may needto be buffed/polished and cleaned before proceeding to a next operationin the process of making an integrated circuit device. Once complete,the wafer is cut into dies, each die representing one integrated circuitchip. The chips are then placed into suitable packages and integratedinto a desired end device, such as a consumer electronic end product.

In summary, the present invention provides methods and apparatus forpolishing, buffing, scrubbing, and rinsing wafers and other suitablesubstrates. The invention has been described herein in terms of severalexemplary embodiments. Other embodiments of the invention will beapparent to those skilled in the art from consideration of thespecification and practice of the invention. The embodiments andpreferred features described above should be considered exemplary, withthe invention being defined by the appended claims.

What is claimed is:
 1. A method for preparing a semiconductor wafer, themethod comprising: disposing a pair of wafer preparation assemblies inan opposing relationship in an enclosure, each of the wafer preparationassemblies having a first wafer preparation member and a second waferpreparation member; disposing a semiconductor wafer between the waferpreparation assemblies in a vertical orientation; rotating the wafer;orienting the wafer preparation assemblies such that the first waferpreparation members contact opposing surfaces of the rotating wafer inan opposing relationship; and orienting the wafer preparation assembliessuch that the second wafer preparation members contact opposing surfacesof the rotating wafer in an opposing relationship, wherein the wafer ismoved in a vertical direction while in contact with the first waferpreparation members or the second wafer preparation members.
 2. Themethod of claim 1, wherein each of the first wafer preparation membersis a cylindrical brush, and each of the second wafer preparation membersis a cylindrical polishing pad.
 3. The method of claim 1, wherein eachof the first wafer preparation members is a cylindrical polishing pad,and each of the second wafer preparation members is a cylindrical brush.4. The method of claim 1, wherein each of the first and second waferpreparation members is a cylindrical brush.
 5. The method of claim 1,wherein each of the first and second wafer preparation members is acylindrical polishing pad.
 6. The method of claim 1, wherein the waferpreparation assemblies are disposed such that the first waferpreparation members are located above the second wafer preparationmembers.
 7. A method for preparing a semiconductor wafer, the methodcomprising: disposing a semiconductor wafer in a vertical orientation inan enclosure; performing a cleaning operation on the wafer in theenclosure using a pair of cylindrical brushes; and performing apolishing operation on the wafer in the enclosure using a pair ofcylindrical polishing pads.
 8. The method of claim 7, wherein the waferis moved in a vertical direction during the polishing operation.
 9. Amethod for polishing a semiconductor wafer, the method comprising:disposing a semiconductor wafer in a vertical orientation in anenclosure; rotating the wafer; performing a first polishing operation onthe rotating wafer in the enclosure using a first pair of cylindricalpolishing pads; and performing a second polishing operation on therotating wafer in the enclosure using a second pair of cylindricalpolishing pads.
 10. The method of claim 9, wherein the first polishingoperation is configured to remove a desired amount of wafer material andthe second polishing operation is configured to provide a desiredsurface finish.
 11. The method of claim 9, wherein the wafer is moved ina vertical direction during at least one of the first hand secondpolishing operations.
 12. The method of claim 9, wherein the first andsecond pairs of cylindrical polishing pads contact opposing surfaces ofthe wafer in an opposing relationship.
 13. The method of claim 9,wherein the first and second pairs of cylindrical polishing pads aredisposed on opposing wafer preparation assemblies, with each of thewafer preparation assemblies having one of the first pair of cylindricalpolishing pads and one of the second pair of cylindrical polishing padsdisposed thereon.
 14. The method of claim 13, wherein the first andsecond pairs of cylindrical polishing pads are brought into contact withopposing surfaces of the wafer by orienting the wafer preparationassemblies.
 15. A method for preparing a semiconductor wafer, the methodcomprising: disposing a semiconductor wafer in a vertical orientation inan enclosure; performing a first wafer preparation operation on thewafer in the enclosure using a first pair of wafer preparation members;and performing a second wafer preparation operation on the wafer in theenclosure using a second pair of wafer preparation members, wherein thefirst and second pairs of wafer preparation members are disposed onopposing wafer preparation assemblies, with each of the waferpreparation assemblies having one of the first pair of wafer preparationmembers and one of the second pair of wafer preparation members disposedthereon.
 16. The method of claim 15, wherein the first wafer preparationoperation is a cleaning operation and the first pair of waferpreparation members is a pair of cylindrical brushes, and the secondwafer preparation operation is a polishing operation and the second pairof wafer preparation members is a pair of cylindrical polishing pads.17. The method of claim 15, wherein the first wafer preparationoperation is a first cleaning operation and the first pair of waferpreparation members is a first pair of cylindrical brushes, and thesecond wafer preparation operation is a second cleaning operation andthe second pair of wafer preparation members is a second pair ofcylindrical brushes.
 18. The method of claim 17, wherein the firstcleaning operation is configured to remove relatively coarse particlesand the second cleaning operation is configured to remove relativelyfine particles.